Recovery of hydrocarbons from underground formations by in situ combustion



June 4, 1968 R E. KUNETKA 3,335,504

RECOVERY OF HYDROCARBONS FROM UNDERGROUND FORMATIONS BY IN SITU COMBUSTION Filed Dec. 29, 1965 3 Sheets-Sheet 1 4 2 t 0 e 5 m 6 w 8 5 N ..m a e 3 M h M S W3 F D N U o R G E. KUNETKA RECOVERY OF HYDROCARBONS FROM UNDER BY IN SITU COMBUSTION Filed Dec. 29, 1965 June 4, 1968 E. KUNETKA June 4, -1 968 R.

' RECOVERY OF HYDROCARBONS FROM UNDERGROUND FORMATIONS BY IN SITU COMBUSTION Filed D80. 29, 1965 3 Sheets-Sheet I:

United States Patent RECOVERY OF HYDROCARBONS FROM UNDERGROUND FORMATIONS BY m SITU COMBUSTION Robert E. Kunetka, Houston, Tex., assignor to Texaco Inc., New York, N.Y., a corporation of Delaware Filed Dec. 29, 1965, Ser. No. 517,249 12 Claims. (Cl. 166-2) ABSTRACT OF THE DISCLOSURE A method of increasing the sweep efficiency across a pattern of wells by concurrent and/or countercurrent in situ combustion wherein the functions of the wells are changed at appropriate times in order to develop a linelike combustion front that approaches a row of production wells from both sides thereof.

In the production of hydrocarbons from permeable underground hydrocarbon bearing formations, it is customary to drill one or more boreholes or wells into the hydrocarbon bearing formations and produce hydrocarbons, such as oil, through designated production wells, either by the natural formation pressure or by pumping the wells. Sooner or later, the flow of hydrocarbons diminishes and/or ceases, even though substantial quantities of hydrocarbons are still present in the underground formations.

Many procedures have been employed for recovering the remaining hydrocarbons, among them the igniting and burning of hydrocarbons in situ within the permeable underground formations, whereby hot gas is generated to force hydrocarbons in the formations toward production wells. While such in situ combustion has been quite successful in secondary recovery, it has been much less than 100% efficient because the combustion front tends to progress through the formations along locally channeled paths from the area of injection to the production area, thus bypassing substantial volumes of hydrocarbons in the formation, rather than sweeping the hydrocarbons as a bank from a broad area of the formation.

It is an object of the present invention to provide a novel in situ combustion procedure, involving a well pattern arrangement, employing both concurrent and countercurrent in situ combustion in such a way as to exploit substantially the entire pattern arrangement in a depleted reservoir with established gas saturation, and to produce almost all of the hydrocarbons remaining in place in the formation. This is accomplished by changing the function of wells in the pattern at strategic times in order to gain maximum control of the fire front.

In its broader aspects, the novel procedure for recovering hydrocarbons by in situ combustion from a gas pervious underground formation comprises establishing a well pattern wherein a plurality of wells are arranged in lines or rows parallel to the coordinate axes of a rectilinear grid, set up for a line drive. The wells can be of /2, l, 5 or acre spacings. In both aspects of the procedure, alternate lines of wells are shut in or are inactive during the first phase, while either concurrent or countercurrent in situ combustion is initiated in the bound ing lines of wells, in which alternate wells are respectively injection wells and production wells.

In the concurrent in situ combustion aspect of the procedure, upon breakthrough of the combustion front at the production wells, these production wells are changed to injection wells, the original injection wells are shut in, and production of hydrocarbons is initiated at the alternate lines of originally shut in or inactive wells.

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In the countercurrent in situ combustion aspect of the procedure, upon completion of the combustion front between the injection and production wells, the production wells are changed to injection wells and injection also is continued in the original injection wells, and production is started in the alternate lines of the original inactive wells. Thus, in both aspects of the invention, due to the high gas permeability in the desaturated burned out zones, a continuous injection surface exists between lines of production wells.

In both aspects of the procedure, there may be an additional step of presaturation by air, so that upon breakthrough of air at the production wells, either concurrent or countercurrent in situ combustion process is initiated, with changes in the well functions being made at appropriate times.

The objects, advantages and features of the invention will become apparent from consideration of the specification in the light of the figures of the drawings, wherein:

FIG. 1 depicts a pattern for an in-line in situ combustion drive, showing the end of the first phase of the concurrent in situ combustion aspect of the procedure which has been completed between the injection and production wells, symbols representing the boreholes or wells penetrating into the underground formation;

FIG. 2 shows the end of the second phase of the concurrent in situ combustion aspect of the procedure indicating the manner in which the combustion front thereof is postulated to proceed away from the lines of injection in both directions towards the adjacent lines of production wells, the formation undergoing concurrent in situ combustion with respect to the production wells of the second phase;

FIG. 2a is comparable to FIG. 2, showing the postulation of the movement of the in-line combustion front when the formation undergoes countercurrent in situ combfistion with respect to the production wells of the second p ase;

FIG. 3 corresponds to FIG. 1 and indicates the end of the first phase of the countercurrent in situ combustion procedure which has been completed between the injection and production wells;

FIG. 4 shows the end of the second phase of the countercurrent in situ combustion aspect of the procedure showing the postulation of the movement of the combustion front continued as a concurrent in situ combustion with respect to the production wells of this phase; and

FIG. 4a is comparable to FIG. 4, showing the postulation of the movement of the in-line combustion front when the formation undergoes countercurrent in situ cornbustion with respect to the production wells of this phase.

The objects of the invention are achieved by developing a line of burned out areas from which a line like combustion front may approach a line of production wells from both sides thereof.

The first phase of the first aspect of the procedure, wherein concurrent in situ combustion in the formation is initiated, is illustrated in FIG. 1, showing a series of injection and production wells arranged in elongated patterns, such as the lines A-A, parallel to the axis of abscissas, wherein alternate wells in each line are injection wells 10, and the remaining wells 20 in the same line are production wells. These wells are also aligned in rows, parallel to the axis of ordinates, which intersect the elongated patterns rectilinearly as illustrated, although, depending on field conditions, they may intersect at other angles. Thus, the injection wells are aligned along the rows BB, and the production wells are aligned along the rows C-C.

Between the elongated patterns or lines A-A, FIG. 1, there are alternate elongated patterns or lines of shut in or inactive Wells 30, during the first phase, which are indicated as arranged in the lines DD, medially between lines AA. These wells are also aligned parallel to the aligned rows of injection and production wells, depicted as arranged in the rows D'D' and also intersect the elongated patterns rectilinearly, although. they may be at some other angle in accordance with field conditions. These inactive wells are staggered with respect to the injection and production wells. Wells 10, 20 and 30 are shown symbolically in the drawings, and only single identifications of the several elongated patterns and aligned rows are shown. The numbering of wells is maintained the same in both phases of the procedure even though the symbols are changed in accordance with the changes in well functions.

At the start of this aspect of the invention, the wells 30 in the alternate elongated patterns or lines DD are shut in, the injection wells of the lines A-A (aligned along the rows BB), are supplied with a combustion supporting fluid, such as air, oxygen, enriched gas or other combustible material, after which ignition of the formation hydrocarbons in initiated, with concurrent pro duction at the production wells along the rows CC. Concurrent in situ combustion occurs, with the typical dual cusp pattern of burnt out areas represented by the cross-hatched areas X, indicating breakthrough of the combustion front at the production wells at the end of the first phase of this aspect of the invention.

it may be desired, prior to initiation of the in situ com bustion, to presaturate the formation with air to produce hydrocarbons from the area in which the burn will be initiated later, corresponding substantially to the double cusp patterns indicated at X. The in situ combustion initiated at the injection wells will follow invariably the area of presaturation and the burn will be accomplished more efiiciently. In summary of this first phase of the in vention, a straight concurrent in situ combustion occurs with injection and ignition initiated at the wells 10, production at the wells 20 until breakthrough of the combustion front, the burned out areas beim indicated by the cross-hatched area X, while the wells 3% are shut in, so that at breakthrough at the production welis, there is developed a continuous injection line between the shut in wells, corresponding to an infinite number of drilled injection wells.

At the beginning of the second phase of this aspect of the procedure employing concurrent in situ combustion, the injection wells 10 of the first phase are shut in, the production wells 20 of the first phase are converted into injection wells, shown situated along the rows CC of FIG. 2, and the shut in wells of the first phase become the producing wells of the second phase of the concurrent in situ combustion, these wells being positioned along lines DD, FIG. 2, and aligned in the rows D'-D, FIG. 2. The in situ combustion front continues to this new row of production wells, and as depicted in FIGS. 1 and 2, there is a line of high gas permeability with injection surfaces at high temperature, so that the burn pattern is outward toward the new lines of producing wells, as indicated by the arrows W, FIG. 2. This pattern leaves sufficient oil saturation at the production wells 20 of FIG. 1 for reignition, if temperatures have fallen at the boundaries of the crosshatched area. The method of operation from the end of a first phase will be concurrent combustion towards the producing wells 30 of the second phase, if the temperatures have remained high enough on the boundary of the burned-out portions to result in a line drive. This would be a most efiicient operation and spacing of the injection and production wells governing the breakthrough time would determine if the temperatures remain high enough for a subsequent line drive concurrent in situ combustion. An equal spacing of the shut in wells 30 (later to become producing wells) between the injection wells 10 and the production wells 20 is indicated, but it may be advantageous to have a close spacing Cir of the wells 10 and 2t e.g., ft., for rapid development of a continuous line of burned out high temperature formations, then a considerably larger spacing between these lines of injection and production wells 10 and 20, viz. lines AA and the lines of shut in wells 30, viz. lines DD, e.g., 600-1000 ft. for the second phase of the operation. If the unfortunate circumstance should arise that the developed high temperature zone along the lines AA be below ignition temperature when the second phase of the procedure is attempted, ignition could be reinitiated at the areas of residual oil saturation at the production wells 20 of the first phase of the operation. Should there be a short spacing between the injection and production wells 19 and 20 compared to the spacing between the lines of wells AA and DD, FIG. 1, a line drive will develop with relatively small loss in sweep efliciency. The areas of residual hydrocarbons remaining at the end of the second phase are indicated by the ellipsoids U, FIG. 2, which are spaced consecutively along lines DD, and are aligned along rows BB and CC, both FIG. 2.

Alternatively, at the beginning of the second phase, the injection wells it) of the first phase could retain their original functions, the production wells 20 of the first phase would be converted into injection wells, and the shut in wells of the first phase would become the production wells of the second phase of the concurrent in situ combustion.

Provided sutlicient combustion supporting gas is available, countercurrent combustion could be initiated at the shut in wells 30 when they are changed to production wells, with some change in sweep efiiciency resulting. The areas of residual hydrocarbons remaining after such a sweep, viz. by countercurrent in situ combustion initiated at the production wells 30 of the second phase of the procedure, are shown in postulated idealized forms at V and V, FIG. 2a, spaced alternately along lines D-D and each respectively along rows BB and CC, FIG. 2a.

FIGS. 3 and 4 disclose phases of a second aspect of invention, wherein a conutercurrent in situ combustion is practiced to form an in-line combustion front. In FIG. 3, there is indicated symbolically injection wells 110, production wells 120 and shut in or inactive 'wells in the first phase of the procedure, 130. The injection and production wells are disposed alternately in the elongated patterns and distributed along the lines indicated as AA, in the same position shown along the lines AA, FIG. 1. Between the lines of injection and production wells, there is disclosed a grouping of wells in an elongated pattern wells in these lines D-D, being aligned With those in the adjacent lines of wells, such as AA. This is seen when reference is made to the rows B'B and C'C' showing the alignment with alternate spacing of injection and shut in or inactive wells and production and inactive wells.

With continued reference to FIG. 3, there is disclosed the end of the first phase of the countercurrent in situ combustion between the injection wells and the production wells 120, with completion of the combustion front between the production and injection wells, the burned area being indicated by the crosshatched areas Y, the time for the completion being indicated with the arrival of high temperatures at the production wells 120.

FIG. 4 discloses the end of the second phase of the countercurrent in situ combustion aspect of the invention which is continued as a concurrent in situ combustion. This is achieved by switching the function of the production wells of FIG. 3 to operate as injection wells as indicated along the rows C'C' of FIG. 4, so that the burnt out areas at Y are essentially a line of injection wells, to provide in elfect a continuous injection line facing the previously inactive wells situated in the lines DD, FIG. 3, which now will function as production wells in FIG. 4. Thus, the line of opened high temperature zones as developed by countercurrent combustion between the wells 110 and 120 advances with a subsequent line drive in a concurrent fashion towards the line of wells along the lines DD. The areas of residual hydrocarbons at the end of this phase of the procedure are disclosed at Z, continuously spaced along the lines DD and aligned between the rows B'-- and C'C, FIG. 4.

With respect to the spacing of the wells 110, 120 and 130 of FIG. 4, the discussions with respect to the spacings of the wells in FIGS. 1 and 2 apply equally well here.

While FIG. 4 discloses concurrent in situ combustion between the symbolically indicated injection wells 110 and 120 and the production wells 130 in this aspect of the invention, if a high oxygen content is produced in the wells 130 along the lines DD, then countercurrent combustion could be initiated at the producing Wells 130' and would result in the areas of residual hydrocarbons as postulated ideally to exist as disclosed at Z in FIG. 4a, spaced along lines DD and aligned between the rows B'-B' and C'-C.

If the production is at high temperature at the end of the first phase of this aspect of the invention, viz, FIG. 3, no attempt at countercurrent combustion at the inactive wells of that phase of the invention would be successful, since the gas entering these previously inactive wells to serve as production wells is stripped of free oxygen. If the temperatures in the areas Y of FIG. 4 are too low for combustion, countercurrent combustion may be initiated at the production wells 130, but for eflicient sweep, these wells should be spaced closely relative to the spacing between the wells in lines AA and DD.

Thus there has been shown and described two aspects of in situ combustion patterns by which an in-line in situ combustion front is used for increasing the sweep efl'iciency, with the functions of the wells being changed during the drive to sweep out areas previously unswept.

Obviously, other modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. In a method of producing a reservoir of an underground hydrocarbon bearing formation by an in-line in situ combustion front wherein a plurality of wells grouped into a plurality of parallel elongated patterns penetrate into said reservoir, the wells in said elongated patterns being aligned in .parallel rows intersecting said patterns angularly, wells in alternate elongated patterns being inactive in the initial phase of the production procedure, alternate wells in said elongated patterns bounding said alternate elongated patterns of inactive wells being injection and production wells respectively, the steps com: prising (a) injecting combustion supporting fluid and initiating in situ combustion at said injection wells in said elongated patterns bounding said alternate elongated patterns while concurrently producing hydrocarbons through said production wells therein,

(b) after breakthrough of the combustion front resulting from said in situ combustion at said production wells, ceasing the producing of hydrocarbons thereat while continuing the injection of said combustion supporting fluid into said injection wells,

(c) producing said inactive wells in said alternate elongated patterns while injecting combustion supporting fluid into the original production wells, with said in situ combustion continuing as an in-line combustion front toward the present production wells from both sides thereof.

2. In the method as defined in claim 1, the wells in said elongated patterns bounding said alternate elongated patterns being staggered with respect to the wells in the last mentioned patterns.

3. In the method as defined in claim 1, said elongated patterns and the aligned rows defining a rectilinear grid,

said in situ combustion being concurrent with respect to said production wells.

4. In the method as defined in claim 1, wherein said elongated patterns and the aligned rows define a rectilinear grid, the additional step (d) of initiating countercurrent in situ combustion at said present production wells.

5. In the method as defined in claim 1, the initiating of in situ combustion of step (a) occurring after the breakthrough of said combustion supporting fluid at said production wells.

6. In the method as defined in claim 1, step (-b) including the ceasing of the injecting of combustion supporting fluid at said injection wells, and thereafter shutting in said injection Wells.

7. In a method of producing hydrocarbons from an underground hydrocarbon bearing formation by an in-line in situ combustion front wherein a plurality of wells grouped into a plurality of parallel elongated patterns penetrate into said formation, the wells in said elongated patterns being aligned in parallel rows intersecting said patterns angularly, wells in alternate elongated patterns being inactive in the initial phase of the production procedure, alternate wells in said elongated patterns bounding said alternate elongated patterns being injection and production wells respectively, the steps comprising (a) injecting combustion supporting fluid at said injection wells in said elongated patterns bounding said alternate elongated patterns and initiating counterourrent in situ combustion at said production wells therein and thereafter concurrently producing hydrocarbons through said production wells,

(b) after completion of said countercurrent in situ combustion between said injection and said production wells and formation of a combustion front therebetween, ceasing producing hydrocarbons at said production wells and thereafter injecting said combustion supporting fluid therethrough and continuing injecting said fluid at said injection wells, and

(c) thereafter producing said inactive wells in said alternate patterns with said in situ combustion of the initial phase continuing as an in-line combustion front toward the present production wells from both sides thereof, and being concurrent with respect thereto.

8. In the method as defined in claim 7, the Wells in alternate aligned rows being alternately inactive and injection wells and inactive and production wells, said elongated patterns and said aligned rows defining a rectilinear grid, the additional step (d) of initiating countercurrent in situ combustion at present production wells.

9. In a method for exploiting an underground hydrocarbon bearing formation by an in-line combustion front wherein bounding lines of wells are parallel to a coordinate axis with alternate wells in said bounding lines of wells being injection and production wells and other lines of wells positioned medially between said bounding lines of wells being shut in during the first production phase, the steps comprising injecting combustion supporting fluid into and igniting said formation at said injection wells in a row of wells adjacent each side of the line of shut in wells and concurrently producing hydrocarbons at said production wells therein until completion of an in-line combustion front between said injection wells and said production wells on each side of said line of shut in wells, and thereafter shutting in said injection wells and opening the wells in said other lines of wells to production, meanwhile injecting said fluid through the original production wells while said in-line combustion front advances toward the present line of production wells from each side thereof.

10. In the method as defined in claim 9, igniting of said formation at said injection wells occurring at breakthrough -of said fluid at said production wells and thereafter continuing injecting fluid at said injection wells.

11. In a method for exploiting an underground hydrocarbon bearing formation by bounding lines of wells parallel to a coordinate axis and other lines of wells positioned medially between said bounding lines of wells being shut in during the first production phase, alternate wells in said bounding lines of wells being injection wells and production wells, the steps comprising injecting combustion supporting fluid into said injection wells in at least two rows of wells in said bounding lines and igniting formation hydrocarbons at said production wells therein and concurrently producing hydrocarbons therefrom until formation of an in-line combustion front between said injection wells and said production wells on each side of the line of shut in wells, thereafter changing the function of said production wells to injection Wells and injecting said fluid therethrough, and opening and producing from the shut in wells as said in-line combustion front approaches from each side thereof, meanwhile continuing 8 injecting said combustion supporting fluid through the original injection wells.

12. In the method as defined in claim 11, the spacing of the injection and production wells in the lines thereof being closer than the spacing of the wells in the other lines of wells.

References Cited UNITED STATES PATENTS 3,057,403 10/1962 Wy llie 166-11 X 3,152,638 10/1964 Geffen et al. 166-11 X 3,153,448 10/1964 Dew et a1. 166-11 X 3,167,117 1/1965 Santounian 166-11 X 3,246,693 4/1966 Crider 166-11 X 3,253,652 5/1966 Connally et a1 166-11 X STEPHEN I. NOVOSAD, Primary Examiner. 

